Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. Referring to FIG. 2, a prior art system 200 associated with an engine is shown. The system 200 is referenced with respect to a centerline/axis 202. For example, the components of the system 200 that are described below are arranged relative to the axis 202 as shown in FIG. 2.
The system 200 is shown as part of a two-spool configuration that includes a first, low speed shaft 214 and a second, high speed shaft 220. The shafts 214 and 220 are rotatably supported by a plurality of bearings contained within a bearing compartment 224.
In FIG. 2, various locations of the engine are denoted by letters A-D. At each of these locations A-D, a pair of seals are shown. Seals are used in the system 200 to isolate a fluid from one or more areas/regions of the engine. Seals control various parameters (e.g., temperature, pressure) within the areas/regions of the engine and ensure proper/efficient engine operation and stability. At location A, an air seal 230a and an oil seal 234a are shown. At location B, an air seal 230b and an oil seal 234b are shown. At location C, an air seal 230c and an oil seal 234c are shown. At location D, an air seal 230d and an oil seal 234d are shown.
The seals 230a and 234a are used to seal the bearing compartment 224 with respect to the shaft 214. The seals 230d and 234d are used to seal the bearing compartment 224 with respect to the shaft 220. The seals 230b, 234b, 230c, and 234c are used to provide intershaft sealing between the shafts 214 and 220, in an area/region where the shafts 214 and 220 interact with or surround one another.
A buffer source 228-1 provides air that interfaces to/between each of the pairs of seals (e.g., air seal and oil seal) at the respective locations A-D. Conventionally, the buffer source 228-1 originates from one or more stages of a low pressure compressor (LPC), such as for example an axially aft-most stage of the LPC. In some instances, the air from the buffer source 228-1 may be at a greater pressure than the air pressure associated with a high pressure compressor (HPC) source 228-2, such that air may flow from the buffer source 228-1, across the air seals 230b and 230c, and into the sink represented by the HPC 228-2. In other instances, the air from the buffer source 228-1 may be at a lower pressure than the air pressure associated with the high pressure compressor (HPC) source 228-2, such that air may flow from the HPC source 228-2, across the air seals 230b and 230c, and into the sink represented by the buffer source 228-1. Typical, commercially available off the shelf (COTS) seals that may otherwise be used for the air seals 230b and 230c may not be configured to operate in such a manner, such that the air flowing across the air seals 230b and 230c as described above may degrade the service lifetime of such air seals 230b and 230c and/or render the air seals 230b and 230c inoperative, increasing pressure in the sink represented by 228-1. This increased pressure may further degrade oil seals 234b and 234c such that there may be an increased risk/potential of oil leaking out of the bearing compartment 224.